1. Field of the Invention
The present invention relates to recording/reproduction devices, and more particularly, to a recording/reproduction device used as a storage device for storing data more accurately, such as the storage device of an information processing apparatus of computers.
2. Description of the Background Art
A digital audio tape recorder (referred to as DAT hereinafter) is a magnetic recording/reproduction device that records audio signals as digital data on a magnetic tape and reads out digital data from a magnetic tape. Such a DAT is used in data recording/reproduction devices for the backup of magnetic disc devices of computers accounting for its large recording capacity and low cost of bit storage. The necessity of recording data onto the magnetic tape of the DAT without an error is vital to DATs used for backup due to the functional characteristics of computers. The following methods are employed to improve the accuracy of recording data in DATs.
An intricated error correction code (parity bit) is added for each predetermined bit length of data applied to a DAT. This error correction code is recorded in a magnetic tape as a digital data along with the actual data to be recorded. At the time of data reproduction of that tape, the error correction code added at the time of recording is detected from the data read out from the magnetic tape. Determination is made whether there is an error in the recorded data excluding the error correction code (the actual recorded data), and the position of the error bit in the reproduced data is detected, according to the detected error correction code. When there is some error in the reproduced data, the data of the bit having its position detected on the basis of the error correction code is corrected to a proper data. Thus, the recorded data in a DAT can be improved in accuracy because an erroneous data recorded in a magnetic tape is corrected at the time of data reproduction.
For the purpose of improving accuracy of recorded data in a DAT by correcting erroneous recorded data at the time of data recording, a method of data recording called the read-after-write method is employed which reads data right after its recording to verify whether the data is properly recorded or not according to the read data. This data recording of the read-after-write method is implemented by a reproduce head tracing a recording track on the magnetic tape following a recording head at the time of data recording. Since data is recorded on the recording track traced by a recording head, the reproduce head tracing the recording track right after the recording head will read out the data recorded immediately before. It can be verified whether data is correctly recorded on the magnetic tape or not according to the data read out by the reproduce head. If the data is not recorded correctly on the magnetic tape, the data applied to the recording head is controlled so that the recording head will record the same data again on the magnetic tape. If data is correctly recorded on the magnetic tape, the data applied to the recording head is controlled so that the recording head will record on the magnetic tape new data. Thus, data will always be recorded correctly on the magnetic tape.
The following methods of determining whether there is an error in the recorded data according to the data read out by a reproduce head in the read-after-write method are described.
An error correction code (parity bit) is added in advance to the data to be recorded, so that this error correction code is detected from the data read out by the reproduce head. Detection is made whether there is an error in the data recorded actually on the magnetic tape, and also the position of the erroneous bit if any, according to the detected error correction code. If there is an error in the data actually recorded on the magnetic tape, the recording head will trace again the area where the erroneous data is recorded. At this time, identical data is applied to the recording head so that the record data on the magnetic tape is rewritten with the correct data.
According to the above described method of using an error correction code, determination is made that there is an error in the recorded data in the case where a portion of data is not at all recorded on a magnetic tape. This is because the output of the reproduce head tracing the region where data is not recorded on the magnetic tape differs from that corresponding to the actual record data. The recording head will trace again the portion where that data is not recorded to carry out accurate data recording. Therefore, correct data can be recorded again on a magnetic tape when there is a missing portion in the data on a magnetic tape, or when erroneous data is recorded on a magnetic tape. A method of verifying whether there is a missing portion on the data recorded on a magnetic tape comprises a method of verifying the envelope of the output signal of the reproduce head (referred to as reproduction signal hereinafter). This method will be described briefly hereinafter.
Digital recording onto a magnetic tape is carried out by positively or negatively magnetizing a magnetic tape, using a recording head, corresponding to binary data of logic values 1 or 0 to be recorded. When the reproduce head traces the magnetized portion on the magnetic tape, voltage is induced in the coil of the reproduce head by magnetic flux leaking out from the magnetic tape. The polarity of the voltage induced in the coil of the reproduce head changes in response to the change of the magnetization polarity of the magnetic tape. The voltage induced in the coil of the reproduce head is the output signal, i.e. the reproduced signal of the reproduce head. The reproduced signal obtained from the region where data is recorded on the magnetic tape shows change in polarity according to the alignment of logic values 1 and 0 of the recorded data to indicate a continuous envelope. The region not having data recorded is not magnetized, so that voltage of either plurality will not be induced in the coil of the reproduce head tracing that region. In the continuous detection of the envelope of the reproduced signal from the reproduce head at the time of data recording of the read-after-write method, the envelope of the reproduced signal will be interrupted corresponding to the time period where the reproduce head is tracing the area where data is not recorded. It is therefore appreciated that the area thereof does not have data recorded. In the case of interruption in the detected envelope according to the continuous detection of the envelope of the reproduced signal, the recording head traces again the area where data is missing on the magnetic tape to re-record the missing data.
The envelope of a reproduced signal is detected by an analog circuit called an envelope detector implemented with a rectifying circuit for full-wave rectification of an input signal, and a low-pass filter for smoothing the output of the rectifying circuit.
The generation of a region where data is not recorded in a magnetic tape which the recording head is tracing occurs, for example, when a foreign substance is introduced into the gap portion of the recording head to temporarily clog the gap portion of the recording head. At the time of data recording, a recording current is provided in the coil of the recording head having the polarity controlled in response to the alignment of logic values 1 and 0 of the recording data to magnetize the magnetic tape. This generates a magnetic field in the gap portion of the recording head, having an intensity sufficient to magnetize the magnetic layer of the surface of the magnetic tape. If the gap portion of the recording head becomes clogged, data recording can not be carried out since a magnetic field of sufficient intensity is not applied to the magnetic tape from the gap portion of the recording head even though recording current is flowing to the coil of the recording head.
There are cases where the data recording of the read-after-write method is employed in a magnetic recording/reproduction device that has to record data very accurately. In such a case, the above described methods of using an error correction code or detecting the envelope of a reproduced signal are employed for verifying the recorded data according to the reproduced signal obtained at the time of data recording. However, the method using an error correction code requires complicated circuitry including a circuit for detecting an error correction code from the reproduced data obtained from a reproduced signal, a circuit for detecting the position of the erroneous data recorded on the magnetic tape according to the detected error correction code, and a circuit for controlling data to be applied to a recording head for recording the proper data on the area where the erroneous data was recorded on the magnetic tape. The method of using an error correction code will increase the circuit complexity in a magnetic recording/reproduction device and the cost thereof.
The method of detecting an envelope of a reproduced signal can be realized by a relatively simple analog circuit, as mentioned above. This method will not induce increase in circuit complexity or cost. However, this method capable of detecting missing recorded data can not detect an error in the recorded data. This gives rise to the following problems.
A case is assumed where data already recorded on a magnetic tape (referred to as former data hereinafter) is rewritten by a new data without erasing the former data, by tracing the recording track where the former data is recorded with a recording head receiving a recording signal corresponding to data to be newly recorded. This data recording method is called the overwrite method. FIG. 7 schematically shows an output of a reproduce head and the envelope thereof when the recording head is temporarily clogged in recording data according to the overwrite method and the read-after-write method in a magnetic recording/reproduction device of R-DAT method.
Since a rotary head is used for both the recording head and the reproduce head in the R-DAT method, a plurality of recording tracks 60 parallel to each other and oblique to the longitudinal direction of a magnetic tape 6 are formed on magnetic tape 6, as shown in FIG. 7(a). At the time of data recording by the read-after-write method, a recording head 61 and a reproduce head 62 sequentially trace each recording track 60. If there is no clog in recording head 61, the record data of the region traced by recording head 61 shows the new data. The output signal of reproduce head 62 tracing this region corresponds to that of the new data. If recording head 61 is temporarily clogged to generate a period in recording track 60 where new data can not be recorded, the data in the region 63 traced by recording head 61 during this period maintains the former data since it is not rewritten with new data. Therefore, the output signal of reproduce head 62 tracing this region corresponds to that of the former data.
The output signal of reproduce head 62, therefore, corresponds to that of the new data during the period where there is no clog in recording head 61, and corresponds to that of the former data during the period where there is a clog in reproduce head 61. (See FIG. 7 (b)). The region 63 traced by recording head 61 during the period where there is a clog in recording head 61 should be detected as a region where data is not recorded correctly. However, region 63 has the former data recorded. The output signal of reproduce head 62 tracing region 63 will show a continuous envelope similar to that of the reproduced signal of reproduce head 62 tracing other regions, i.e. the regions where new data is recorded. The envelope of the output signal of reproduce head 62 is not interrupted during period "a" where there is a clog in recording head 61 which is similar to that of period "b" where there is no clog in recording head 61, as shown in FIG. 7(c). Region 63 having the former data recorded is erroneously determined as having new data recorded. Therefore, the recorded data of region 63 is eventually not correct.
In the case where two rotary heads are used as the recording head, the two recording heads alternately trace recording track 60. For the purpose of preventing crosstalk between adjacent recording tracks 60, the trace angle (azimuth) of the gap portion of one of the two rotary heads for recording a track 60 is designed to be different from that of the other rotary head. It is therefore necessary to trace each recording track with a reproduce head having an azimuth identical to that of the recording head tracing that track at the time of data recording to read a signal recorded in that recording track 60. Accordingly, two rotary heads are used for the reproduce head each having an azimuth identical to that of the respective rotary heads of the recording heads. The two rotary heads alternately trace recording tracks 60 to read a signal. The probability of obtaining a reproduced signal corresponding to the former data from reproduce head 62 tracing region 63 where the former data is recorded as shown in FIG. 7(a) is 1/2.
If the azimuth of the recording head having traced region 63 for recording of the former data into region 63 coincides with that of reproduce head 62 tracing region 63 during recording of new data, a reproduced signal is obtained from reproduce head 62 even during the period where there is a clog in recording head 61. In this case, erroneous determination is made that region 63 actually having the former data recorded has the new data recorded correctly, as described above. If the azimuth of the recording head having traced region 63 during recording of the former data differs from that of reproduce head 62 tracing region 63 during recording of the new data, a reproduced signal is not obtained during the period where there is a clog in recording head 61. In this case, determination is made that the new data is not correctly recorded in region 63, since the envelope of the reproduced signal is interrupted during the period where reproduce head 62 traces region 63 having the former data recorded. According to the method of detecting an envelope of a reproduced signal, a clog in recording head 61 can be detected with a probability of only 50% even in the case where two rotary heads are used for the recording head and the reproduce head respectively.
In the case of data recording by the so-called update-in-place method that selectively rewrites a portion of an already recorded data to a new data, the recording track to be recorded with a new data is traced by a recording head and a reproduce head having an azimuth identical to that of the recording head used in writing the former data therein. In this case, reproduce head 62 tracing region 63 having the former data recorded definitely provides a reproduced signal corresponding to the former data. Therefore, the probability of region 63 having the former data recorded being detected as a portion not having the new data recorded correctly is 0%.
According to the method of making determination whether data is recorded correctly on a magnetic tape using the envelope of a reproduced signal, it is not possible to detect with high accuracy a clog in a recording head occurring at the time of data recording with the overwrite method, for example.